The combustion apparatus of a gas turbine engine is required to operate in such a way that the amount of harmful emissions which it produces is minimised. Unfortunately this requirement is often at odds with the requirement that such the combustion apparatus should operate in as efficient manner as possible. Combustion apparatus efficiency improves with increased temperatures within the apparatus. However such increased temperatures give rise to a correspondingly increased rate in the production of the oxides of nitrogen. Such oxides are looked upon as being highly undesirable emissions.
One factor which is significant in the production of the oxides of nitrogen is the efficiency of the atomisation and evaporation of the fuel which is combusted in the combustion apparatus and the thorough mixing of the fuel with the air which is fed into the combustion chamber for combustion purposes. If the fuel is poorly atomised and evaporated so that liquid fuel droplets remain, or if local areas of high fuel concentration occur, the combustion temperature increases. This in turn results in a correspondingly increased rate in the production of the oxides of nitrogen.